Biofuels and biochemicals derived from lignocellulosic biomass represent an alternative to petroleum-based transportation fuels and other chemicals that take advantage of an abundant and renewable resource while not utilizing food crops as feedstocks. Cellulose and hemicellulose found in biomass, however, must first be converted to fermentable sugars, which are in turn converted to biofuels such as ethanol and biodiesel, and biochemical building blocks such as 3-hydroxypropionic acid, by fermentative organisms.
Several key factors negatively impact the production yield, and thus the cost of biofuels and biochemicals from renewable sources. Common hindrances in the biological production of biofuels and biochemicals include: (1) intermediate and end-product toxicity to the fermentative organisms, (2) the diversion of carbon to biomass formation, and (3) co-production of undesired byproducts, among others. An alternative is to eliminate the fermentative organisms entirely and instead operate the desired metabolic pathway in isolation, thus circumventing the roadblock of biological toxicity and lack of specificity. However, in vitro enzyme systems suffer from low productivities owing in part to the effects of free diffusion of intermediates within metabolic pathways, lack of long term enzyme stability, cofactor cost or inefficient recycling rates, and cost of enzyme production.